folly, tao: don't impose C constraints on folly's Portability.h

folly, tao: don't impose C constraints on folly's Portability.h

Summary:
* folly/Portability.h: Move the definitions that Tao uses
into a new file, and include that new file here.
* folly/AddressSanitizer.h: New file.
* tao/server/config.h: Include that small new file, rather
than all of folly's Portability.h

Test Plan:
fbconfig -r tao/server &&
tao/server/tests/run_unit_tests.sh -d --save-log=log
For folly, watch the arc-run tests.

Reviewed By: pgriess@fb.com

FB internal diff: D1011800

@override-unit-failures